石英に含まれるガラス包有物の主成分分析によるK-Tzの識別

概要

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In strongly weathered tephras, it is commonly the case that only quartz and opaque minerals remain unaltered. For example, the K-Tz tephra is distinguished by abundant quartz crystals. The identification of strongly weathered tephras is difficult because major-element analyses of volcanic glass are affected by weathering. Here, we propose a method of identifying weathered tephras based on major-element analyses of pristine glass inclusions preserved in quartz phenocrysts, and apply the method to identifying the K-Tz, Nr-N, and Kt-1 tephras.We used energy-dispersive X-ray (EDX) techniques to analyze samples of the K-Tz tephra collected from a proximal location (Tanegashima, near Kikai caldera) and from three distal locations. The major-element compositions of glass inclusions are similar in all the K-Tz samples, but are distinct from those of the Nr-N and Kt-1 tephras.Major-element analysis of quartz-hosted glass inclusions is a promising method in investigations of strongly weathered Quaternary tephras in Japan, such as K-Tz.
日本地質学会の論文